A pump impeller

Abstract: The invention concerns a device for a centrifugal pump impeller to be used when pumping polluted liquids. A cover disc (5) on the impeller (3) opposite the inlet (4) is provided with balancing openings (12) for balancing the axial force. The flow (F₂) through said openings is used for rinsing the leading edges (7) of the vanes (6) where pollutions tend to collect.

Description: The invention concerns a pump of a so-called rotodynamic type comprising a rotary impeller in a pump housing. Pumps of this sort may essentially be divided into two types: centrifugal pumps and axial flow pumps. A centrifugal pump impeller with the features of the preamble of claim 1 is known from SU-A-1 751 429, in particular Figs. 2.3 and 2.5. A centrifugal pump comprises an impeller with a hub and at least one cover disc provided with a number of vanes, a so-called open impeller. A so-called closed impeller is provided with two cover discs and intermediate vanes. The liquid is sucked into the center of the impeller in an axial direction and leaves the impeller at the circumference in an essentially tangential direction. The axial flow pump differs from the centrifugal pump in that the liquid leaves the pump in an axial direction. The linking of the liquid is carried out by a number of guide vanes arranged down stream of the pump housing. The guide vanes also normally serve as support elements in the pump construction. When pumping sewage water and water in some types of industrial processes containing fibrous material, it often happens that the pumping is disturbed by rags fibres etc being stuck to the leading edges of the impeller vanes and the guide vanes. The build-up of pollutions may initially cause vibrations in the pumps and eventually worse efficiency and complete clogging. It is sometimes possible to get rid of the pollution by letting the impeller rotate backwards at certain intervals, but this is of course not a satisfactory solution. Another way to diminish the risk for clogging is to provide the pump with cutting means which disintegrate the pollutions before they enter the impeller. An example is shown in the Swedish Patent No 8205774-6. A disadvantage with this solution is that the cutting means may be worn out and after that the clogging problems may get even worse. Other solutions to reduce clogging problems are shown in JP-A-58 192 995 and SU-A-1 143 884. Here, openings are arranged in the impeller where additional flows are created, which are intended to flush pollutants. However, said openings do not obtain this as they are incorrectly positioned. According to the invention, the problem to reduce clogging problems are solved by help of a system of openings in the impeller, which openings are arranged in a special way as stated in the claims. The invention is more closely described with reference to the drawings. Fig 1 shows a partial cut through a centrifugal pump with an impeller according to the invention, Fig 2 shows an enlarged detail, while Fig 3 shows a view of the inlet of the impeller inlet seen from below. In the drawings 1 and 2 stand for the driving unit and the hydraulic unit respective in a submersible centrifugal pump. 3 stands for the pump impeller and 4 its inlet, 5 a cover disc and 6 vanes. 7 stands for the leading edge of a vane 8 its end and 9 its trailing edge. 10 stands for pump housing end wall, 11 a slot, 12 balancing openings, 13 impeller shaft, 14 attaching screw, 15 notches and 16 pump outlet. F 1 , F 2 , F 3 stand for liquid flows. With reference to Fig 1 the centrifugal pump shown comprises an electric driving unit 1 and a hydraulic part, pump housing 2, in which a pump impeller 3 rotates driven via a shaft 13. The impeller sucks the liquid through the inlet 4 and pumps it out through the pump outlet 16. The main flow of the fluid through the impeller is shown by the arrows F 1 . The number of vanes 6 in the pump housing may vary and if a maximum throughlet is desired, for instance when pumping sewage water, an impeller with only a single vane is used. Even then it is very common that when pumping liquids containing fibrous pollutions the latter have a tendency to stick to the leading edges of the vanes 7. Another problem that always occurs at pumping is an axial force which presses the impeller 3 in the direction of the pump inlet 4, thus causing stress on the shaft bearing 13. This problem can be solved, at least partly, by help of balancing openings 12 in the cover disc 5 turned away from the opening, through which openings pumped medium may pass into the inner of the pump housing, arrow F 2 . This technique is well known and by adapting the area of the openings a considerable reduction of the axial force can be obtained. A condition is however that the liquid that passes the balancing openings is relatively clean in order not to clog the relatively narrow openings. This can be obtained by letting a part of the pumped liquid flow through a narrow slot 11 between the cover disc 5 of the impeller and the housing end wall 10, arrow F 3 . The clean liquid which should be fed the narrow slot may also be used for cooling of the electric motor alone or completed with clean water fed from outside. According to the invention the liquid that flows through the balancing openings is also used for rinsing the leading edges of the vanes where pollutions, as previously mentioned are easily collected. For that purpose the balancing openings are so positioned that the flow, arrow F 2 , through the openings will hit the ends 8 of the leading edges 7 of the vanes. The number of openings is normally the same as the number of vanes and the radial positions of the openings in the cover disc are decided by the positions of the leading edges 7 of the vanes. In this way a flow along the leading edge of each vane is obtained which effectively flushes pollutions that tend to stick to the edge and cause functional trouble. A disadvantage when using balancing openings in general is that the flow through them is essentially opposite the main flow F 1 through the impeller which lowers the efficiency. According to a further development of the invention there is a notch 15 provided in the cover disc 5 in the area of each opening 12 so directed, that the flow F 2 is deflected in a direction which more corresponds with the main flow through the impeller, arrow F 1 . This effect is further strengthened according to still another development of the invention, where the attach bolt which locks the impeller 3 to the shaft 13 is designed with a head such, that it covers the notches 15. In this way channels are created which direct the flow F 2 towards the ends of the vane edges and also deflects the flow in a direction which adopts to the main flow F 1 through the impeller. According to the invention a known technique for equalizing of axial forces is used to obtain a simultaneous rinsing of the leading edges of the vanes, thus diminishing the risks for operation problems and even for a total clogging of the pump housing. By help of further developments of the invention stated in claims 2 and 3 a certain increase of the efficiency is obtained.

Claims: A centrifugal pump impeller for pumps to be used for pumping polluted liquids such as waste water, said impeller (3) comprising at least one cover disc (5) attached to a driving shaft (13), one or several vanes (6) mounted on the disc and a central, axially directed inlet (4), the disc opposite said inlet being provided with balancing openings (12) for reduction of the axial force that occurs during operation, characterized in, that the balancing openings (12) are positioned very close in front of the leading edges (7) of the vanes (6), each opening (12) radially inwards of a corresponding leading edge (7), for letting the flow through said openings rinse said edges. A centrifugal pump impeller according to claim 1, characterized in, that the cover disc (5) is provided with notches (15) at the openings (12), which notches guide the flow from said openings towards the leading edges (7) of the vanes. A centrifugal pump impeller according to claim 1, characterized in, that the impeller (3) is attached to the driving shaft (13) by help of a bolt, the head (14) of which is radially extended to partly cover the notches (15) for additional guiding of the flow from the openings (12) in a direction which approaches the main flow F1 through the impeller.

Inventors: BRANDT BENGT-AKE, BRANDT, BENGT-AKE
Applicants: FLYGT AB ITT, ITT FLYGT AKTIEBOLAG
Application year: 1994
Main classification: F04D29
IPC codes: F04D29